Microwave phase shifter with liquid dielectric having metallic particles in suspension

ABSTRACT

Microwave phase shifters and electronic beam steering antennas are described which use an electrically controllable anisotropy dielectric medium in the microwave beam path.

United States Patent Harold T. Buscher Berkeley, Calif.

Feb. 16, 1970 Dec. 28, 1971 General Dynamics Corporation Inventor Appl.No. Filed Patented Assignee MICROWAVE PHASE SHIFIER WITH LIQUIDDIELECTRIC HAVING METALLIC PARTICLES IN SUSPENSION 31 Claims, 13 DrawingFigs.

U.S. Cl 343/754, 343/854, 343/872, 343/909, 333/31 A, 333/98 P Int. Cl...H01q 19/06 Field of Search 343/753, 754, 755, 909, 910, 911, 854,872; 333/31, 31 A,

PROPAGATION DIRECTION [56] References Cited UNITED STATES PATENTS1,945,039 1/1934 Hansell 343/909 2,223,950 12/1940 Brown.. 343/7563,408,653 10/1968 Blass 343/754 3,434,138 3/1969 Shostak 343/911 PrimaryExaminer-Eli Lieberman Art0rneyMartin Lu Kacher ABSTRACT: Microwavephase shifters and electronic beam steering antennas are described whichuse an electrically controllable anisotropy dielectric medium in themicrowave beam path.

VARIABLE Bl SUPPLY WAVEF RONT PATENTEnutczsisn 3 531 50 SHEET u 0F 4FIG. 41.

I NVE N TOR. HAROLD Z' BUSCHER A TTORNE Y MICROWAVE PHASE SIIIFIERWITI-I LIQUID DIELECTRIC HAVING METALLIC PARTICLES IN SUSPENSION Thepresent invention relates to microwave components and particularly to anelectro-optical control system for microwaves.

The present invention is especially suitable for use in electronic beamsteering antennas such as may be used in airborne radar systems. Theinvention is also suitable for providing microwave phase shiftcomponents. Aspects of the invention will be generally applicable forother microwave control purposes.

Conventional means for the control of microwave energy to provide phaseshift and electronic beam steering are subject to several limitations.Devices which use ferrite phase shift elements as exemplified bythe beamsteering array described in U.S. Pat. No. 3,305,867, issued Feb. 21,1967, to A. R. Miccioli and Donald H. Archer, are heavy and there arelimitations upon power handling capacity, as well as accuracy of angularcontrol over beam direction. The cost of such conventional equipment isalso high.

Attempts to use other means have also not been entirely successful.lonizable gases are suggested in U.S. Pat. No. 3,404,401, issued Oct. 1,1968, to M. Arditi. Such devices require a high amount of power tomaintain the gas discharge. Heating of-the device proscribes its use inmany applications. In addition, the electron discharge absorbs much ofthe microwave energy which it is intended to control.

A mechanical device using movable resonators is described in U.S. Pat.No. 2,840,820, issued to G. C. Southworth on June 24, 1958. Deviceswhich use mechanical resonance have a limited frequency range, andusually require bearings and the like, which are difficult, if notimpossible to fabricate in production.

Accordingly, it is an object of the present invention to provideimproved apparatus for electro-optical control of microwave energy.

It is a further object of the present invention to provide improvedelectro-optical apparatus for the control of microwave energy which isreadily adaptable to provide beam steering of radar beams.

It is a still further object of the present invention to provideimproved apparatus for electro-optical control of microwave energy whichis not affected by the microwave energy which it is intended to control.

It is a still further object of the present invention to provide animproved electro-optical beam steering antenna which has fast responseand therefore provides a rapid scan of the microwave beam.

It is a still further object of the present invention to provide animproved electro-optical beam steering antenna and phase shiftingdevices which are capable of handling high microwave power.

It is a still further object of the present invention to provideimproved electro-optical apparatus for microwave control purposes whichis lighter in weight and may be fabricated at lower cost thanconventional apparatus which has been provided for the purpose.

It is a still further object of the present invention to provide animproved electro'optical microwave control system which does not usemechanically movable parts.

path and is electronically controlled to vary the propagation velocityof the microwave energy. Thus, it produces a phase shift or delay. Anarray of cells including the dielectric medium which is disposed in thepath of a microwave beam may be controlled to steer the beam on transmitor to steer the directional response on receive so that an electronicscanning antenna is provided. More particularly, the dielectric mediummay contain conductive particles having a normally random orientationwhich normally renders the medium isotropic. When an electric field isapplied to the medium, the particles polarize and align their long axiswith the control field, thus changing the path permittivity of themedium in the control field direction (viz the medium is madeanisotropic). The

It is a still further object of the present invention to provide degreeof statistical alignment and therefore the change in permittivity isrelated to the strength of the control field. The microwave energyitself does not disturb the particle alignment because the inertia ofthe particles and the viscosity of the medium in which they aresuspended is such that the particles can not respond to thehigh-frequency microwave energy, especially when that energy is in pulseform (viz, pulses of less than 500 microsecond duration).

The invention itself, both as to its organization and method ofoperation, as well as additional objects and advantages thereof willbecome more readily apparent from a reading of the following descriptionin connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic view of a microwave energy control cellprovided in accordance with the invention, the view illustrating inperspective the basic geometry of the cell;

FIG. 2 is a graph showing the phase shift characteristics of a cell ofthe type illustrated in FIG. 1;

FIG. 3 is a side view of a section of microwave waveguide, the guidebeing broken away to illustrate the apparatus contained within' thewaveguide which provides a microwave phase shifter in accordance withthe invention;

FIG. 4 is a end view of the waveguide shown in FIG. 3, partially brokenaway to illustrate the phase shifting elements in greater detail;

FIG. 5 is a fragmentary top view of the device shown in FIG.

FIG. 6 is a front view of a microwave phase shifter in accordance withanother embodiment of the invention;

FIG. 7 is a top view of the phase shifter shown in FIG. 6;

FIG. 8 is an exploded view, fragmentarily showing the phase shiftershown in FIGS. 6 and 7;

FIG. 9 is a front view of an electronic beam steering antenna providedin accordance with the invention, the view being broken away to betterillustrate the internal construction thereof;

FIG. 10 is a left side view of the antenna shown in FIG. 9, alsopartially broken away to illustrate the internal construction thereof;

FIG. 11 is a perspective view of a beam steering antenna similar to theantenna shown in FIG. 9 which is provided in accordance with anotherembodiment of the invention;

FIG. 12 is a perspective view of another beam steering antenna which isprovided in accordance with another embodiment of the invention; and

FIG. 13 is a left side view partially broken away to illustrate a radomestructure which also provides a beam steering anten-' na in accordancewith another embodiment of the invention.

Referring more particularly to FIG. 1, there is shown a cell 10 filledwith a dielectric medium and having a pair of control electrodes 12 and14 on opposite sides thereof. These electrodes define the area of thecell. The cell controls the phase shift of a microwave signal which isillustrated as a TEM-mode signal. The vecto r k is the direction ofpropagation of the signal. The F and H vectors of the signal are alsoillustrated. A variable voltage bias source is connected to theelectrodes 12 and 14 so as to produce and establish a bias or controlfieltL Note that the field direction is parallel to the direction of theE vector of the microwave signal.

The dielectric medium may be a dielectric liquid which fills the cell.The liquid contains conductive particles which are desirably microscopicin size and are also desirably asymmetrical in shape (e.g., needles ordiscs). The properties of the suspension (its mass density, viscosity,loss tangent and dielectric constant) determine, together with thestrength of the bias field, the phase shift or delay produced by thecell. The bias field may be a DC field; however, an AC field is muchmore preferable. This field may have a frequency which is very low ascompared to the frequency of the microwave energy. Suitable frequencyfor the AC control field is 20 kHz. Among the features of the deviceare:

l. Lightweight, both as to the device itself and the circuitry whichcontrols it.

2. Relative simplicity and low cost.

3. Reciprocity for at least one polarization of the microwave signal.

4. Electrostatically controllable with very low control powerconsumption. 7

5. Substantially independent of temperature, humidity and stray magneticfields.

6. High efficiency and low insertion loss, even at high microwavefrequencies (e.g., i(,u-band frequencies and higher), since a negligibleamount of microwave energy is absorbed in the cell.

7. Capability to provide 360 phase shift control.

8. Readily and continuously adjustable throughout its control range.

9. Rapid response time.

l0. Capability of handling very high power (e.g., several hundredkilowatts per square centimeter power loading).

11. inert chemically, so that it is fireproof and does not release toxicgases or liquids.

The characteristics of the dielectric medium in the cell shall now beconsidered. In a preferred form of the invention, the dielectric mediumis a suspension in a base liquid which is nonpolar, has substantiallyzero conductivity and low permittivity. The suspended particles areconductive material. They may be needles or filaments 2 microns indiameter and 200 microns long (the dimensions being given here solelyfor purposes of illustration). The particles may also be discs, whichconfiguration is presently preferred. Thus, the particles are small ascompared to a wavelength of the microwave energy. Under quiescentconditions, the particles are randomly oriented so that the suspensionis statistically isotropic. The apparent permittivity of the suspensionmay be calculated approximately in accordance with the followingequation:

where e is the apparent permittivity 6,, is the permittivity of freespace a, is the dipole polarizability of each particle, and

N is the particle number density For highly-conductive particles whichare right circular cylinders, 200 microns long and 2 microns indiameter, and for a liquid which has a dielectric constant of 1.85, thevalue of N required to provide 360 phase control over a 3-cm. pathlength is 3.3 X10 per cubic centimeter. For particles, such as siliconcarbide whiskers having mass density of 3.12, the number of particlesnecessary to satisfy the foregoing value of N weighs 0.67 mg. It willtherefore be apparent that the cell may be extremely light in weight andyet will provide a large amount of phase control.

The viscosity of the liquid is an important criteria. it is importantthat the particles not be affected by the microwave energy, while theyat the same time have rapid response to the bias field. A 0.8 centistokeliquid viscosity has been found suitable. The rotational viscous dragdue to the liquid is essentially negligible for field intensities of thebias field of approximately 1 kilovolt per centimeter. The response timeis therefore rapid. Rotation of the particles (in response to the field)to any desired orientation can be accomplished in a matter ofmilliseconds, even for extremely high particle densities. The viscositymentioned above is also important since it makes the settling rate (dueto gravity) of the particles extremely slow. For example, for a 0.85centistoke viscosity, the settling rate is about 0.2 centimeters perhour. As will be explained hereinafter, the use of surfactants reducesthe settling rate to a degree where it is negligible so far as operationof the system is concerned.

The chemical structure of the suspension is dictated by a need for lowinsertion loss (viz, low absorption of the microwave energy). It hasbeen found that fluorocarbon liquids and some hydrocarbon liquids, suchas benzene, are especially suitable. The filamentary or whiskerparticles of silicon carbide and boron nitride, as mentioned above, aresuitable. It is. however, preferable to use microscopic discs ofaluminum (viz, 1 micron diameter).

in order that the particles be extremely miscible in the liquids, asurfactant (surface-active-agent) to wet and stabilize the particles inthe liquid is desirable. The liquid should be nonionic. Accordingly, thechoice of surfactants is limited to those which do not release anysignificant quantity of ions into the liquid. Aluminum octoate has beenfound to be a suitable surfactant when aluminum discs are used asparticles. The following table lists examples of suspensions which maybe used in practicing the invention. it will be appreciated, of course,that other suspensions and dielectric mediums may be provided inaccordance with the invention.

Base liquid Particle Surfactant material material (chemical (massdensity) (mass density) name) Genesolv-D 200p. needles of Span 60trichlorotrifiuoroethanc silicon carbide (sorbiton mono- (1.57) (3.12)stearate) Triton (IF-10 (alkyl aryl ether) Triton X405 Naccolene A(modified petroleum sulfonate) Quaternary O (quaternized amine, 0)

Cerasynt SE (glycerol and y g ycol stearate) in diameter Aluminumoctoate t aluminum discs (2.7) Benzine Aluminum octoate (0.88)

PN-43O (alkyl polyoxyethyleneamine) Tergitol NP-27 (alkyl phenylpolyethylene V Y glycol other) I O-43 Fluorocarbon 1e diameter Stearieacid (1.88) aluminum discs Tetrabromocthanc ZOOu needles of Cerasynt M(2.96) silicon carbide (glycol stearate) Tctrabromocthanc 200, needlesof 0.12. Hall No. (2.96) silicon carbide 123 FC78 Fluorocarbon 20011-needles of FC-134 (1.7) silicon carbide (3-M Co.

3.12 proprietary) FIG. 2 demonstrates the amount of phase shift which isobtained with different dielectric media. Three curves are illustrated.The greatest amount of phase shift being obtained from the dielectricmedium which is a liquid suspension of aluminum particles in afluorocarbon (Freon 1 148-2 having 10 milligrams per cubic centimeter ofaluminum particles which are made miscible by the addition of lmilligram per cubic centimeter of the 3M Company FX-l 73 surfactant).

Another advantage of the AC control field over DC control fields is theavoidance of net sweeping effects and convection of the particles due tothe slight, nearly unavoidable traces of free ions in the liquid. Theuse of the low-frequency AC control fields greatly reduces such sweepingand prolongs the suspension lifetime (viz, reduces settling rate). Thesurfactants have an additional effect in improving the phase shiftcharacteristics. It is believed, and this belief is expressed solely forpurposes of explaining the invention and without implying anyrestriction to any particular theory of operation, that the surfactantproduces a chemical charge micelle surrounding each particle The higherthe micelle charged density, the larger will be the achievable phaseshift. Certain liquids, such as Freon 1i4B2 and Genesolv-D appear toenhance the chemical charge micelle effect.

Sources of the various liquids and surfactants are as follows:

Genesolv-D is manufactured by the Allied Chemical Corp. of Los Angeles,California.

Span-60 is manufactured by the Atlas Chemical Industries of Wilmington,Delaware.

Triton is manufactured by the Atlas Chemical and Manufacturing Companyof San Diego, California.

Naccolene is manufactured by the Allied Chemical Corporation of LosAngeles, California.

Freon is manufactured by the Dupont Company of Wilmington, Delaware.

FC-43 and FC-78 and FC-l38 are manufactured by the 3M Company of St.Paul, Minnesota.

Katapol PN-430 is manufactured by the General Aniline 8L FilmCorporation of New York, New York.

Cerasyant is manufactured by the Van Dyk & Company of Belleville, NewJersey.

Tergitol is manufactured by the Union Carbide Corporation of New York,New York.

Referring to FIGS. 3, 4 and 5, there is shown a waveguide microwavephase shifter in accordance with the invention. A rectangular guidesection 18 is a top wall 20 and a bottom wall 22, as well as sidewalls24 and 26. The wide top and bottom walls have circular openings 28 and30 therein in alignment with each other.

Flanges 32 and 34 are connected to the guide 18 at the opposite endsthereof. These flanges afford means for connections to other sections ofwaveguides, as is shown in phantom in FIGS. 6 and 7. A pair of plates 38and 40 extend the length of the guide 18, as well as into the flanges 32and 34. These plates provide the control electrodes of the phase shifterand may be connected to a variable voltage source for creating the biasfield. The plates are surrounded by sheets of dielectric material, 42,44, 46 and 48. The sheets 42 and 48 insulate the electrodes from thewalls of the guide 18. The sheets 44 and 46 prevent any contamination ofor conduction current through the dielectric liquid which fills theguide by the metal plates 38 and 40. Discs 50 and 52 of dielectricmaterial which are fitted into the choke groove 54 and over the endsurfaces of the flanges 32 and 34 secure the liquid in place. Thesediscs 50 and 52 also provide windows through which the electromagneticwaves may enter the phase shifter. The sheets 40 to 48 and the windows50 and 52 are desirably of polytetrafluoroethylene material such as ofthe type which is commonly known as Teflon" sold by the E. I. DuPontDeNeumours Company. The plates 38 and 40 and the waveguide walls 20 and22 which are separated by the Teflon sheets 42 and 48 providecapacitors. These capacitors have substantially no reactance atmicrowave energy frequency. Accordingly, the plates 38 and 40 will beessentially at the same potential as the waveguide walls for microwavefrequencies. However, at the alternating current frequencies which areused to develop the bias field, the Teflon sheets 42 and 48 provide goodinsulators.

The microwave phase shifter operates essentially, as was described inconnection with FIG. 1. Briefly, the particles in the suspension alignthemselves with the field, thereby making the suspension anisotropic andincreasing its permeability, the amount of anisotropy being a functionof the field intensity (viz the voltage applied across the plates 38 and40).

Another embodiment of the microwave phase shifter is shown in FIGS. 6, 7and 8. Like the phase shifter shown in FIGS. 3-5, this phase shifter hasa flanged waveguide section 60 with a top wall 62, a bottom wall 64 andsidewalls 66 and 68. The top and bottom walls 62 and 64 have alignedrectangular openings 70 and 72 therein. The sheets of insulatingmaterial 74 and 76 cover these openings, but extend somewhat beyond theedges thereof. Control electrodes in the form of plates 78 and 80 ofsubstantially the same size as the dielectric sheets 74 and 76 areplaced over these sheets and secured by suitable fastening means, suchas clamps (not shown), onto the guide 60. The guide section covered bythe plates 78 and 80 is sealed by windows 82 and 84 of dielectricmaterial (e.g., Teflon), so as to define the cell which is filled with adielectric liquid suspension containing particles, as was described inconnection with FIG. 1.

A capacitor is defined around the rim area of the plates 78 and 80, bythe rim area of the sheets 74 and 76 and the top and bottom walls theguides 62 and 64. This capacitor has a low reactance to microwaveenergy; thus placing the plates 78 and 80 at essentially the samepotential as the walls of the guide for microwave energy.

A bias field may be applied to the plates by way of leads 88 and 90. Theoperation of the phase shifter in response to the bias field is as wasdescribed in connection with FIG. 1.

Referring to FIGS. 9 and 10, there is shown an electronically steerableantenna which utilizes a plurality (an array) of cells of the type shownin FIG. 1. A container which may be a Teflon shell contains these cells.The cells are formed by columns of individual control electrode plates102 which are separated from each other and aligned in columns. Theplates are thin strips of a highly conductive material, such asaluminum. Connections are made to each of the plates through feedthroughcapacitors 104.

Between the columns of plates 102 are disposed thin strips 106 ofconductive material such as aluminum. Each plate and the conductivestrips adjacent thereto defines a cell. Two of these cells 108 and 110are depicted by the dash line squares in FIG. 9.

The backwall 112 of the container 100 has a sheet of conductivematerial, such as a reflecting backing of copper or aluminum foilthereon. The front wall 114 of the container 100 is desirably providedwith an impedance matching device 116 made up of conical dielectric rodswhich interface between the air and the dielectric of the phaseshifters. The container is filled with a dielectric medium, such as thesuspension, as described in connection with FIG. I.

In operation, a feed such as the horn 120 projects a beam of microwaveenergy toward the container 100. This energy is matched impedance-wiseto the beam scanning structure by means of the cones 116. The beampasses into the container and the cells therein and is reflected by thefoil backing Ill. The control system which is connected to the controlelectrode plates 102 applies different voltages to these plates,depending upon the direction in which the beam is to be steered. Ifnecessary, a varying control potential may be applied to the plates inorder to cause the beam to sweep or scan, either conically or linearly.The reflected beam, as shown by the line 122 is therefore steered in thedesired direction. A computer may be used to control the voltage levelsapplied to various control electrode plates 102. This computer may besimilar to that described in connection with FIGS. 10 and II of theMiccioli et al. patent referenced above. The programmer controlsvoltages rather than currents, inasmuch as the beam steering device iselectrostatically operated in the case of the device in FIGS. 9 and 10.

FIGS. 11, 12 and I3 illustrate different embodiments of the beamsteering antenna in accordance with the invention. The beam steeringstructure 130, shown in FIG. 11, is disposed on a concave parabolicsupport I32. A feed horn I34 projects a beam of microwave energy ontothe beam steering device and the beam is reflected therefrom in themanner described in connection with FIGS. 9 and W. Inasmuch as thestructure I30 is parabolic, the same control potentials as are used insteering the beam in the embodiment of FIGS. 9 and It) will provide aconically scanned or swept but narrowly focused beam for the parabolicconfiguration of FIG. I I.

In FIG I2, a source of microwave energy I40 drives a feed horn M2. Abeam steering device 144 which is associated with the radar equipmentforming part of the source 1144 is similar to that shown in connectionwith FIGS. 9 and M), except that the reflecting foil backing is omitted.Accordingly, the microwave beam projected by the feed M2 passes directlytherethrough. This transmission system also serves to steer the beam.

FIG. 13 shows a radome made up of a substantially conical structure 150containing an array of cells formed by the electrode plates and stripssimilar to those shown in FIGS. 9 and 10. The surfaces of the strips andcontrol electrode plates are disposed approximately perpendicular to theinner surface of the radome. A radar set I52 provided with a feed 154,projects a beam through the radome beam steering structure. This beam issteered by varying the control potentials applied to the controlelectrode plates thereof.

From the foregoing description, it will be apparent that there has beenprovided improved electro-optical apparatus suitable for microwave phaseshifting and beam steering. It will be observed that the radar apparatusshown in FIGS. 9 through I3, while described in connection with a radartransmitter is equally applicable for reception of radar beams. Thedirectivity (viz, directional response of the radar) is adjustable bycontrolling the beam steering device to provide a predetermined lookangle, which angle can be swept across the area of interest byprogramming the control potentials. Other variations and modificationswithin the scope of the invention will undoubtedly suggest themselves tothose skilled in the art. Accordingly, the foregoing description shouldbe taken merely as illustrative and not in any limiting sense.

What is claimed is:

E. An electromagnetic wave control apparatus which comprises meanscontaining a suspension comprising a dielectric medium having asymmetricconductive particles freely and isotropically suspended therein, theviscosity of said medium and the moment of inertia of said particlesbeing such that the motion of said particles is substantiallyunresponsive to said wave when propagated therethrough, and means forchanging the permittivity of said suspension for controlling thepropagation of said wave therethrough wherein said permittivity chargingmeans includes means for orienting said suspension to become anisotropicfor a time which is long with respect to the frequency of said waves.

2. The invention as set forth in claim I wherein said time is providedby means which applies an AC field of a frequency which is low withrespect to said electromagnetic wave frequency across said suspension.

3. The invention as set forth in claim I wherein said permittivitychanging means comprises means for applying an electric field acrosssaid suspension for orienting said particles so that their longestdimension is aligned in the same direction as a component of theelectromagnetic field corresponding to said wave.

4. The invention as set forth in claim 3 wherein said particles arenonmagnetic.

5. The invention as set forth in claim 4 wherein the majority of saidparticles are elongated in shape.

6. The invention as set forth in claim 3 wherein means are included insaid field applying means for varying said field in intensity.

'7. The invention as set forth in claim 4 wherein said particles arecrystal whiskers.

8. The invention as set forth in claim 7 wherein said whiskers are ofsilicon carbide.

9. The invention as set forth in claim 4 wherein said particles arefilamentary in form.

it). The invention as set forth in claim I wherein said medium is anonionic dielectric liquid.

31 l. The invention as set forth in claim 10 wherein said liquid issomewhat viscous.

12. The invention as set forth in claim 11 wherein the viscosity of saidliquid is on the order of 0.8 centistoke.

I3. The invention as set forth in claim I0 wherein said liquid isprincipally a composition selected from the class of fluorocarbons andhydrocarbons.

M. The invention as set forth in claim 13 wherein said liquid iscomposed principally of a fluorocarbon.

15. The invention as set forth in claim 13 wherein said liquid isbenzene.

to. The invention as set forth in claim 13 wherein said liquid includesalso a surfactant.

117. The invention as set forth in claim 17 wherein said surfactant isaluminum octoate.

18. The invention as set forth in claim 10 wherein said particles have anumber density of about 3.3 X10 per cm.

I9. The invention as set forth in claim 10 wherein said particles arealuminum discs.

2d). The invention as set forth in claim 19 wherein said discs are lessthan l micron in diameter.

211. A microwave phase shifter which comprises a. a waveguide,

b. a pair of control electrodes deposited in spaced relationshipopposite to each other to define a gap therebetween, said gap beinglocated within said waveguide, said electrodes also being disposed ininsulating relationship with said waveguide,

c. means for confining within said guide and in said gap a suspension ofconductive particles of microscopic size in an inert viscous liquidhaving low permittivity, said suspension being isotropic until saidelectrodes provide a field across said gap for rendering said suspensionanisotropic, the amount of anisotropy being related to the phase shiftproduced by said phase shifter.

22. The invention as set forth in claim 21 wherein said waveguide isrectangular in shape and has wide top and bottom walls and narrowersidewalls, each of said wide walls have openings therein which areopposite each other, said control electrodes being plates disposedagainst said wide walls and covering said openings, and sheets ofdielectric material separating each said plates from their adjacentwall.

23. The invention as set forth in claim 22 wherein said plates and saidsheets extend beyond the edges of said openings to define capacitiveelements with the portions of said wide walls adjacent thereto, saidelements having a reactance which is negligible at microwave frequenciessuch that said electrodes and said waveguide are at essentially the samepotential at microwave frequencies.

24. The invention as set forth in claim 22 wherein said plates aredisposed outside said waveguide.

25. The invention as set forth in claim 22 wherein said plates aresubstantially the same width as said wide walls of said guide and extendalong a section of said guide longer than said guide is wide.

26. The invention as set forth in claim 22 including a pair of windowsof dielectric material across the cross section of said guide onopposite sides of said gap for confining said suspension in said guide.

27. Apparatus for electrically steering a microwave beam which comprisesa. means disposed in the path of said beam containing a suspension ofmicroscopic conductive particles in a liquid having low permittivity andpredetermined viscosity such that said suspension is isotropic in thepresence of said beam,

b. an array of cells in said containing means, said cells beingcomprised of individual control electrodes which are spaced from eachother, and

c. means for applying control potentials separately to said electrodesfor providing selectively variable anisotropy in different portions ofsaid containing means whereby to steer said beam.

28. The invention as set forth in claim 27 wherein said containing meanshas opposite front and back surfaces disposed successively in the pathof said beam, said back surface being reflective to said microwaveenergy and said front surface being transmissive thereto.

29. The invention as set forth in claim 28 further comprising a feedprojecting said beam in a first direction into said containing means soas to enter first said front surface and then said back surface so as tobe reflected therefrom in a second direction opposite to said firstdirection, said control means being operative to cause said beam to scanin directions transverse to said first direction whereby to provide ascanning antenna.

30. The invention as set forth in claim 27 wherein said controlelectrodes are plates of conductive material arranged edgewise to liealong the axis of said beam, said plates being disposed in columns withthe plates in each column in alignment with each other, and strips ofconductive material also disposed edgewise to lie along the axis of saidbeam, said strip being disposed between said columns of electrodes sothat each plate and the strips on opposite sides thereof form individualones of said cells.

31. The invention as set forth in claim 30 wherein said containing meanshas a conicallike form, a feed disposed to pro ject said beam into thearea circumscribed by said form along the axis thereof whereby saidcontaining means provides a radome.

1. An electromagnetic wave control apparatus which comprises meanscontaining a suspension comprising a dielectric medium having asymmetricconductive particles freely and isotropically suspended therein, theviscosity of said medium and the moment of inertia of said particlesbeing such that the motion of said particles is substantiallyunresponsive to said wave when propagated therethrough, and means forchanging the permittivity of said suspension for controlling thepropagation of said wave therethrough wherein said permittivity chargingmeans includes means for orienting said suspension to become anisotropicfor a time which is long with respect to the frequency of said waves. 2.The invention as set forth in claim 1 wherein said time is provided bymeans which applies an AC field of a frequency which is low with respectto said electromagnetic wave frequency across said suspension.
 3. Theinvention as set forth in claim 1 wherein said permittivity changingmeans comprises means for applying an electric field across saidsuspension for orienting said particles so that their longest dimensionis aligned in the same direction as a component of the electromagneticfield corresponding to said wave.
 4. The invention as set forth in claim3 wherein said particles are nonmagnetic.
 5. The invention as set forthin claim 4 wherein the majority of said particles are elongated inshape.
 6. The invention as set forth in claim 3 wherein means areincluded in said field applying means for varying said field inintensity.
 7. The invention as set forth in claim 4 wherein saidparticles are crystal whiskers.
 8. The invention as set forth in claim 7wherein said whiskers are of silicon carbide.
 9. The invention as setforth in claim 4 wherein said particles are filamentary in form.
 10. Theinvention as set forth in claim 1 wherein said medium is a nonionicdielectric liquid.
 11. The invention as set forth in claim 10 whereinsaid liquid is somewhat viscous.
 12. The invention as set forth in claim11 wherein the viscosity of said liquid is on the order of 0.8centistoke.
 13. The invention as set forth in claim 10 wherein saidliquid is principally a composition selected from the class offluorocarbons and hydrocarbons.
 14. The invention as set forth in claim13 wherein said liquid is composed principally of a fluorocarbon. 15.The invention as set forth in claim 13 wherein said liquid is benzene.16. The invention as set forth in claim 13 wherein said liquid includesalso a surfactant.
 17. The invention as set forth in claim 17 whereinsaid surfactant is aluminum octoate.
 18. The invention as set forth inclaim 10 wherein said particles have a number density of about 3.3 X 104per cm.3.
 19. The invention as set forth in claim 10 wherein saidparticles are aluminum discs.
 20. The invention as set forth in claim 19wherein said discs are less than 1 micron in diameter.
 21. A microwavephase shifter which comprises a. a waveguide, b. a pair of controlelectrodes deposited in spaced relationship opposite to each other todefine a gap therebetween, said gap being located within said waveguide,said electrodes also being disposed in insulating relationship with saidwaveguide, c. means for confining within said guide and in said gap asuspension of conductive particles of microscopic size in an inertviscous liquid having low permittivity, said suspension being isotropicuntil said electrodes provide a field across said gap for rendering saidsuspension anisotropic, the amount of anisotropy being related to thephase shift produced by said phase shifter.
 22. The invention as setforth in claim 21 wherein said waveguide is rectangular in shape and haswide top and bottom walls and narrower sidewalls, each of said widewalls have openings therein which are opposite each other, said controlelectrodes being plates disposed against said wide walls and coveringsaid openings, and sheets of dielectric material separating each saidplates from their adjacent wall.
 23. The invention as set forth in claim22 wherein said plates and said sheets extend beyond the edges of saidopenings to define capacitive elements with the portions of said widewalls adjacent thereto, said elements having a reactance which isnegligible at microwave frequencies such that said electrodes and saidwaveguide are at essentially the same potential at microwavefrequencies.
 24. The invention as set forth in claim 22 wherein saidplates are disposed outside said waveguide.
 25. The invention as setforth in claim 22 wherein said plates are substantially the same widthas said wide walls of said guide and extend along a section of saidguide longer than said guide is wide.
 26. The invention as set forth inclaim 22 including a pair of windows of dielectric material across thecross section of said guide on opposite sides of said gap for confiningsaid suspension in said guide.
 27. Apparatus for electrically steering amicrowave beam which comprises a. means disposed in the path of saidbeam containing a suspension of microscopic conductive particles in aliquid having low permittivity and predetermined viscosity such thatsaid suspension is isotropic in the presence of said beam, b. an arrayof cells in said containing means, said cells being comprised ofindividual control electrodes which are spaced from each other, and c.means for applying control potentials separately to said electrodes forproviding selectively variable anisotropy in different portions of saidcontaining means whereby to steer said beam.
 28. The invention as setforth in claim 27 wherein said containing means has opposite front andback surfaces disposed successively in the path of said beam, said backsurface being reflective to said microwave energy and said front surfacebeing transmissive thereto.
 29. The invention as set forth in claim 28further comprising a feed projecting said beam in a first direction intosaid containing means so as to enter first said front surface and thensaid back surface so as to be reflected therefrom in a second directionopposite to said first direction, said control means being operative tocause said beam to scan in directions transverse to said first directionwhereby to provide a scanning antenna.
 30. The invention as set forth inclaim 27 wherein said control electrodes are plates of conductivematerial arranged edgewise to lie along the axis of said beam, saidplates being disposed in columns with the plates in each column inalignment with each other, and strips of conductive material alsodisposed edgewise to lie along the axis of said beam, said strip beingdisposed between said columns of electrodes so that each plate and thestrips on opposite sides thereof form individual ones of said cells. 31.The invention as set forth in claim 30 wherein said containing means hasa conicallike form, a feed disposed to project said beam into the areacircumscribed by said form along the axis thereof whereby saidcontaining means provides a radome.